As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
Based on their external and internal structures, secondary batteries are generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Especially, the prismatic battery and the pouch-shaped battery, which can be stacked with high integration and have a small width to length ratio, have attracted considerable attention.
Also, the secondary batteries have attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, kinds of applications using the secondary batteries are being diversified owing to advantages of the secondary batteries, and hereafter the secondary batteries are expected to be applied to more applications and products than now.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery will be heated or explode due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) for effectively controlling the abnormality of the lithium secondary battery, such as overcharge, is mounted in the lithium secondary battery while the PCM is connected to a battery cell of the lithium secondary battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current conduction, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery cell to prevent the explosion or the overheating of the battery cell, the leakage of liquid from the battery cell, and the degradation of the charge and discharge characteristics of the battery cell, and to suppress the lowering of the electrical efficiency of the battery cell and the abnormal physicochemical behavior of the battery cell, thereby eliminating dangerous factors from the battery cell and increasing the service life of the battery cell.
Generally, the PCM is electrically connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to connection leads of the PCM by welding or soldering, and then the nickel plates are connected to corresponding electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
In this case, a large number of welding or soldering processes are required to construct the battery pack, and the welding or soldering processes must be carried out with high precision because of the small structure of the secondary battery. As a result, a defect possibility is great. Furthermore, the welding or soldering processes are added during the manufacturing process of a product, which increases the manufacturing costs.
Also, it is required for safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, a plurality of insulative mounting members are required to achieve such connection, with the result that the battery cell assembling process is complicated. On the other hand, an adhesive may be applied between the safety elements and the insulative mounting members to achieve the coupling between the safety elements and the insulative mounting members. However, this coupling method weakens the strength of the battery cell. Consequently, an electric short circuit may occur in the battery cell due to the weakening of the coupling strength, when external impacts are applied to the battery cell, with the result that the battery cell may catch fire or explode. In other words, safety-related problems may occur.
Therefore, research has been actively made on various technologies for easily assembling the insulative mounting members and the safety elements loaded at the top of the battery cell and, at the same time, increasing the mechanical strength of the battery pack.
In connection with this matter, for example, Korean Patent Application Publication No. 2006-0060801 discloses a secondary battery including an electrode group consisting of a separator and a cathode plate and an anode plate disposed on opposite sides of the separator, a case in which the electrode group is mounted, a cap assembly coupled to the case for sealing the case, the cap assembly having external terminals electrically connected to the electrode group, gaskets disposed in corresponding external terminal through-holes formed at the cap assembly such that the gaskets are disposed between the corresponding external terminals and the corresponding through-holes, and coupling members fitted on the external terminals such that the coupling members are coupled to the corresponding external terminals in tight contact with the gaskets.
However, it is not possible for the two external terminals, formed at the cap assembly and electrically connected to the electrode group, to fixedly couple the safety elements, including the protection circuit modules, loaded at the top of the battery cell, with the result that it is difficult to increase the mechanical strength of the top of the battery cell.
Also, Korean Patent Application Publication No. 2004-0054232 discloses a secondary battery including an electrode assembly consisting of a cathode plate, an anode plate, and a separator disposed between the cathode plate and the anode plate, a container in which the electrode assembly is received together with an electrolyte, the container being made of a conductive metal material, the container being provided at the bottom thereof with at least one fixing protrusion, a cap plate coupled in an opening formed at the container, the cap plate being provided at one side of the upper part thereof with at least one groove, a cap assembly inserted through the cap plate such that the cap assembly is isolated from the cap plate by a gasket, the cap assembly having an electrode terminal connected to any one of the tabs withdrawn from the cathode and anode plates, and a lead plate coupled in the groove of the cap plate, which is achieved by inserting the lead plate into the groove and pressing the lead plate, the lead plate being connected to a safety device.
The lead plate, coupled in the cap plate by pressing, serves to securely fix the safety device located at the top of the battery cell, thereby somewhat increasing the mechanical strength of a battery pack. However, a protection circuit module is still coupled to the electrode terminals of the battery cell by welding or soldering, with the result that a battery pack assembling process is complicated.
Consequently, there is a high necessity for a technology that is capable of reducing the number of members mounted to the top of the battery cell to simplify the assembling process and achieving the connection between the protection circuit module and the insulative mounting members in a no-welding manner while stably securing the coupling strength therebetween.